U.S. patent application number 16/533735 was filed with the patent office on 2020-02-27 for resistance change device, manufacturing method for the same, and storage apparatus.
This patent application is currently assigned to FUJITSU LIMITED. The applicant listed for this patent is FUJITSU LIMITED. Invention is credited to Hideyuki Noshiro.
Application Number | 20200066338 16/533735 |
Document ID | / |
Family ID | 69586471 |
Filed Date | 2020-02-27 |
![](/patent/app/20200066338/US20200066338A1-20200227-D00000.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00001.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00002.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00003.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00004.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00005.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00006.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00007.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00008.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00009.png)
![](/patent/app/20200066338/US20200066338A1-20200227-D00010.png)
View All Diagrams
United States Patent
Application |
20200066338 |
Kind Code |
A1 |
Noshiro; Hideyuki |
February 27, 2020 |
RESISTANCE CHANGE DEVICE, MANUFACTURING METHOD FOR THE SAME, AND
STORAGE APPARATUS
Abstract
A resistance change device includes a first resistance change
layer that occludes and discharges ions of at least one type, and
resistance of the first resistance change layer, changes in
accordance with an amount of the ions in such a manner that the
resistance decreases when the ions are discharged and the
resistance increases when the ions are occluded; a second
resistance change layer that occludes and discharges the ions, and
resistance of the second resistance change layer changes in
accordance with the amount of the ions in such a manner that the
resistance increases when the ions are discharged and the
resistance decreases when the ions are occluded; and an ion
conductive layer that carries the ions and is provided between the
first resistance change layer and the second resistance change
layer.
Inventors: |
Noshiro; Hideyuki;
(Kawasaki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJITSU LIMITED |
Kawasaki-shi |
|
JP |
|
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
69586471 |
Appl. No.: |
16/533735 |
Filed: |
August 6, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11C 2213/31 20130101;
G11C 13/004 20130101; H01L 45/1233 20130101; H01L 45/147 20130101;
G11C 13/0061 20130101; H01L 45/085 20130101; G11C 13/0069 20130101;
G11C 13/003 20130101; H01L 45/1266 20130101; G11C 2013/005
20130101; G11C 13/0011 20130101; G11C 2013/0045 20130101; G11C
2013/009 20130101; H01L 45/1608 20130101; G11C 2213/52
20130101 |
International
Class: |
G11C 13/00 20060101
G11C013/00; H01L 45/00 20060101 H01L045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2018 |
JP |
2018-157213 |
Claims
1. A resistance change device comprising: a first resistance change
layer that occludes and discharges ions of at least one type, and
resistance of the first resistance change layer changes in
accordance with an amount of the ions in such a manner that the
resistance decreases when the ions are discharged and the
resistance increases when the ions are occluded; a second
resistance change layer that occludes and discharges the ions, and
resistance of the second resistance change layer changes in
accordance with the amount of the ions in such a manner that the
resistance increases when the ions are discharged and the
resistance decreases when the ions are occluded; and an ion
conductive layer that carries the ions and is provided between the
first resistance change layer and the second resistance change
layer.
2. The resistance change device according to claim 1, wherein the
ions discharged from the first resistance change layer pass through
the Ion conductive layer to be occluded in the second resistance
change layer, and the ions discharged from the second resistance
change layer pass through the ion conductive layer to be occluded
in the first resistance change layer.
3. The resistance change device according to claim 1, wherein the
ions discharged from the first resistance change layer pass through
the ion conductive layer to be occluded in the second resistance
change layer, so that both the resistance of the first resistance
change layer and the resistance of the second resistance change
layer decrease, and the ions discharged from the second resistance
change layer pass through the ion conductive layer to be occluded
in the first resistance change layer, so that both the resistance
of the first resistance change layer and the resistance of the
second resistance change layer increase.
4. The resistance change device according to claim 1, wherein
resistance changes occur simultaneously in the first resistance
change layer and the second resistance change layer at a write
time.
5. The resistance change device according to claim 1, wherein the
first resistance change layer is a positive-electrode active
material layer formed of a positive-electrode active material used
in an ion battery, the ion conductive layer is a solid electrolytic
layer formed of a solid electrolyte used in the ion battery, and
the second resistance change layer is a negative-electrode active
material layer formed of a negative-electrode active material used
in the ion battery.
6. The resistance change device according to claim 5, wherein the
positive-electrode active material is one of LiCoO.sub.2,
LiNiO.sub.2, LiTi.sub.5O.sub.12, LiMnO.sub.2, LiFePO.sub.4; the ion
conductive layer is one of Li.sub.3PO.sub.4,
Li.sub.9Al.sub.3(P.sub.2O.sub.7).sub.3(PO.sub.4).sub.2,
Li.sub.2.9PO.sub.3.3N.sub.0.46, (La, Li)TiO.sub.3; and the
negative-electrode active material is Li.sub.4Ti.sub.5O.sub.12.
7. The resistance change device according to claim 1, further
comprising: a first electrode and a second electrode that are
disposed separate from each other and connected to the first
resistance change layer; and a third electrode and a fourth
electrode that are disposed separate from each other and connected
to the second resistance change layer.
8. A storage apparatus comprising: a resistance change device; a
write circuit connected to the resistance change device and
configured to write information into the resistance change device;
and a read circuit connected to the resistance change device and
configured to read out information from the resistance change
device, wherein the resistance change device includes a first
resistance change layer that occludes and discharges ions of at
least one type, and resistance of the first resistance change layer
changes in accordance with an amount of the ions in such a manner
that the resistance decreases when the ions are discharged and the
resistance increases when the ions are occluded, a second
resistance change layer that occludes and discharges the ions, and
resistance of the second resistance change layer changes in
accordance with the amount of the ions in such a manner that the
resistance increases when the ions are discharged and the
resistance decreases when the ions are occluded, and an ion
conductive layer that carries the ions and is provided between the
first resistance change layer and the second resistance change
layer.
9. The storage apparatus according to claim 8, wherein the read
circuit configures the first resistance change layer and the second
resistance change layer to be connected in parallel, and is
configured to read out information by applying a read voltage to
the first resistance change layer and the second resistance change
layer and detecting a current flowing through the first resistance
change layer and the second resistance change layer.
10. The storage apparatus according to claim 8, wherein the read
circuit configures the first resistance change layer and the second
resistance change layer to be connected in series, and is
configured to read out information by applying a read voltage to
the first resistance change layer and the second resistance, change
layer and detecting a current flowing through the first resistance
change layer and the second resistance change layer.
11. The storage apparatus according to claim 8, wherein the
resistance change device includes a first electrode and a second
electrode that are disposed separate from each other and connected
to the first resistance change layer, and a third electrode and a
fourth electrode that are disposed separate from each other and
connected to the second resistance change layer, the write circuit
writes information by applying a write voltage to the first
resistance change layer and the second resistance change layer via
at least one of the first electrode and the second electrode and
via at least one of the third electrode and the fourth electrode to
cause the resistance of the first resistance change layer and the
second resistance change layer to change, and the read circuit
reads information by applying a read voltage to the first
resistance change layer via the first electrode and the second
electrode, also applying the read voltage to the second resistance
change layer via the third electrode and the fourth electrode, and
detecting a current flowing through fire first resistance change
layer and the second resistance change layer.
12. The storage apparatus according to claim 11, wherein the write
circuit applies a positive voltage as a write voltage to at least
one of the first electrode and the second electrode and grounds at
least one of the third electrode and the fourth electrode to cause
a change in resistance of the first resistance change layer and the
second resistance change layer.
13. The storage apparatus according to claim 11, wherein the write
circuit grounds at least one of the first electrode and the second
electrode and applies a positive voltage to at least one of the
third electrode and the fourth electrode to cause a change in
resistance of the first resistance change layer and the second
resistance change layer.
14. The storage apparatus according to claim 8, wherein the ions
discharged from the first resistance change layer pass through the
ion conductive layer to be occluded in the second resistance change
layer, and the ions discharged from the second resistance change
layer pass through the ion conductive layer to be occluded in the
first resistance change layer.
15. The storage apparatus according to claim 8, wherein the ions
discharged from the first resistance change layer pass through the
ion conductive layer to be occluded in the second resistance change
layer, so that both the resistance of the first resistance change
layer and the resistance of the second resistance change layer
decrease, and the ions discharged from the second resistance change
layer pass through the ion conductive layer to be occluded in the
first resistance change layer, so that both the resistance of the
first resistance change layer and the resistance of the second
resistance change layer increase.
16. The storage apparatus according to claim 8, wherein resistance
changes occur simultaneously in the first resistance change layer
and the second resistance change layer at a write time.
17. The storage apparatus according to claim 8, wherein the first
resistance change layer is a positive-electrode active material
layer formed of a positive-electrode active material used in an ion
battery, the ion conductive layer is a solid electrolytic layer
formed of a solid electrolyte used in the ion battery, and the
second resistance change layer is a negative-electrode active
material layer formed of a negative-electrode active material used
in the ion battery.
18. A manufacturing method for a resistance change device, the
method comprising: forming a first resistance change layer to
occlude and discharge ions of at least one type, and resistance of
the first resistance change layer changes in accordance with an
amount of the ions in such a manner that the resistance decreases
when the ions are discharged and the resistance increases when the
ions are occluded; forming, on the first resistance change layer,
an ion conductive layer configured to carry the ions; and forming,
on the ion conductive layer, a second resistance change layer to
occlude and discharge ions, and resistance of the second resistance
change layer changes in accordance with the amount of the ions in
such a manner that the resistance increases when the ions are
discharged and the resistance decreases when the ions are occluded.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2018-157213,
filed on Aug. 24, 2018, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] The embodiments discussed herein are related to a resistance
change device, a manufacturing method for the same, and a storage
apparatus.
BACKGROUND
[0003] Such an information storage device has been proposed that
utilizes a principle of a secondary battery configured to charge
and discharge by the movement of ions between a positive-electrode
active material layer and a negative-electrode active material
layer through an electrolytic layer, and makes use of the
configuration thereof.
[0004] Japanese Laid-open Patent Publication No. 2012-89567 and
Japanese Laid-open Patent Publication No. 2003-157672 are examples
of related art.
SUMMARY
[0005] According to an aspect of the embodiments, a resistance
change device includes a first resistance change layer that
occludes and discharges ions of at least one type, and resistance
of the first resistance change layer changes in accordance with an
amount of the ions in such a manner that the resistance decreases
when the ions are discharged and the resistance increases when the
ions are occluded; a second resistance change layer that occludes
and discharges the ions, and resistance of the second resistance,
change layer changes in accordance with the amount of the ions in
such a manner that the resistance increases when the ions are
discharged and the resistance decreases when the ions are occluded;
and an ion conductive layer that carries the ions and is provided
between the first resistance change layer and the second resistance
change layer.
[0006] The object and advantages of the invention will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0007] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the invention.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a cross-sectional view illustrating a
configuration of a resistance change device according to the
present embodiment;
[0009] FIG. 2 is a diagram illustrating a case where a first
resistance change layer and a second resistance change layer of the
resistance change device according to the present embodiment are
connected in parallel;
[0010] FIG. 3 is a graph depicting changes in resistance of the
resistance change device according to the present embodiment and a
resistance change device of related art;
[0011] FIG. 4 is a cross-sectional view illustrating a
configuration of the resistance change device of related art;
[0012] FIG. 5 is a graph depicting charge and discharge
characteristics of the resistance change device of related art;
[0013] FIG. 6 is a graph depicting charge and discharge
characteristics of the resistance change device according to the
present embodiment;
[0014] FIG. 7 is a diagram illustrating wiring to be connected in
such a manner that the first resistance change layer and the second
resistance change layer are connected to the resistance change
device according to the present embodiment in parallel, and also
illustrating a current flow at a read time;
[0015] FIG. 8 is a diagram illustrating wiring and switches to be
connected to a resistance change device according to the present
embodiment;
[0016] FIG. 9 is a diagram illustrating a configuration of a
storage apparatus according to the present embodiment;
[0017] FIG. 10 is a diagram for describing an information write
operation in a case where the first resistance change layer and the
second resistance change layer of the resistance change device
according to the present embodiment are connected in parallel;
[0018] FIG. 11 is a diagram for describing an information write
operation in a case where the first resistance change layer and the
second resistance change layer of the resistance change device
according to the present embodiment are connected in parallel;
[0019] FIG. 12 is a diagram for describing an information read
operation in a case where the first resistance change layer and the
second resistance change layer of the resistance change device
according to the present embodiment are connected in parallel;
[0020] FIG. 13 is diagram illustrating a case where the first
resistance change layer and the second resistance change layer of
the resistance change device according to the present embodiment
are connected in series;
[0021] FIG. 14 is a diagram illustrating wiring to be connected in
such a manner that the first resistance change layer and the second
resistance change layer are connected to the resistance change
device according to the present embodiment in series, and also
illustrating a current flow at a read time;
[0022] FIG. 15 is a diagram for describing an information write
operation in a case where the first resistance change layer and the
second resistance change layer of the resistance change device
according to the present embodiment are connected in series;
[0023] FIG. 16 is a diagram for describing an information write
operation in a case where the first resistance change layer and the
second resistance change layer of the resistance change device
according to the present embodiment are connected in series;
and
[0024] FIG. 17 is a diagram for describing an information read
operation in a case where the first resistance change layer and the
second resistance change layer of the resistance change device
according to the present embodiment are connected in series.
DESCRIPTION OF EMBODIMENTS
[0025] In a case where the configuration of the secondary battery
mentioned above is applied to a resistance change device included
in a storage apparatus, it is considered that, for example, a
positive-electrode active material layer is used for a resistance
change layer which is able to occlude and discharge ions and in
which resistance is changed in accordance with the amount of ions,
an electrolytic layer is used for an ion conductive layer
configured to carry ions but not carry electrons, and a
negative-electrode active material layer is used for an ion
occlusion and discharge layer that is able to occlude and discharge
ions.
[0026] In this case, due to the movement of ions between the
resistance change layer and the ion occlusion and discharge layer
through the ion conductive layer, the amount of ions in the
resistance change layer varies and the resistance changes in
response to the variation in the amount of ions, which makes it
possible to cause the above configuration to function as a
resistance change device.
[0027] However, since a material having high resistivity is used
for the positive-electrode active material layer, it has been found
that, in the case where the positive-electrode active material
layer is used for the resistance change layer, the resistance
becomes large and the readout current becomes small, thereby
causing a malfunction.
[0028] Hereinafter, using the drawings, a resistance change device,
a manufacturing method for the stated resistance change device, and
a storage apparatus according to an embodiment of the present
disclosure will be described with reference to FIGS. 1 to 17.
[0029] As illustrated in FIG. 1, a resistance change device
according to the present embodiment includes, on a substrate 1, two
resistance change layers (a first resistance change layer 2 and a
second resistance change layer 4) which are able to occlude and
discharge ions of at least one type and in which resistance is
changed in accordance with the amount of ions of at least one type,
and an ion conductive layer 3 that is provided between the first
resistance change layer 2 and second resistance change layer 4, and
carries ions of at least one type.
[0030] Here, the two resistance change layers 2 and 4 are each
formed of a material which is able to occlude and discharge ions of
at least one type, and the resistance of which changes in
accordance with the amount (concentration) of ions of at least one
type. The ion conductive layer 3 is formed of a material configured
to carry ions of at least one type.
[0031] In this case, due to the movement of ions between the first
resistance change layer 2 and second resistance change layer 4
through the ion conductive layer 3, the amount of ions in the first
resistance change layer 2 and second resistance change layer 4
vary, and the resistance thereof changes in response to the
variations in the amount of ions, which makes it possible to cause
the above configuration to function as a resistance change device
9.
[0032] As described above, the resistance change device 9 of the
present embodiment has a structure including two resistance change
layers 2 and 4 on the lower and upper sides with the ion conductive
layer 3 interposed therebetween, in which their resistance values
change in accordance with the composition ratios.
[0033] Note that the ion conductive layer 3 is an ion conductive
layer configured to carry ions of at least one type but not carry
electrons. Further, an ion that moves passing through the ion
conductive layer 3 is also referred to as a conductive ion.
[0034] It is also possible to continuously change the resistance
values of the first resistance change layer 2 and second resistance
change layer 4 by continuously varying the amount of ions in these
layers, and therefore it is possible to achieve a multi-valued
resistance change device able to store a large number of resistance
values.
[0035] In the present embodiment, the first resistance change layer
2 is a layer able to occlude and discharge ions of at least one
type and the resistance thereof changes in accordance with the
amount of ions of at least one type, that is, the first resistance
change layer 2 is a resistance change layer in which the resistance
decreases when the ions of at least one type are discharged, and
the resistance increases when the ions of at least one type are
occluded.
[0036] Here, since the first resistance change layer 2 is disposed
in a lower layer, it is also referred to as a lower-side resistance
change layer or a resistance change layer in the lower layer.
[0037] The second resistance change layer 4 is layer able to
occlude and discharge ions of at least one toe and the resistance
thereof changes in accordance with the amount of ions of at least
one type, that is, the second resistance change layer 4 is a
resistance change layer in which the resistance increases when the
ions of at least one type are discharged and the resistance
decreases when the ions of at least one type are occluded.
[0038] Here, since the second resistance change layer 4 is disposed
in an upper layer, it is also referred to as an upper-side
resistance change layer or a resistance change layer in the upper
layer.
[0039] In the present embodiment, although the first resistance
change layer 2 is disposed under the ion conductive layer 3, in
other words, on the side closer to the substrate 1, and the second
resistance change layer 4 is disposed above the ion conductive
layer 3, in other words, on the side farther from the substrate 1,
the positions of the resistance change layers are not limited
thereto.
[0040] For example, the first resistance change layer 2 may be
disposed above the ion conductive layer 3, in other words, on the
side farther from the substrate 1, and the second resistance change
layer 4 may be disposed under the ion conductive layer 3, in other
words, on the side closer to the substrate 1. That is, the first
resistance change layer 2 may serve as the upper-side resistance
change layer disposed in the upper layer, and the second resistance
change layer 4 may serve as the lower-side resistance change layer
disposed in the lower layer.
[0041] The ions discharged from the first resistance change layer 2
pass through the ion conductive layer 3 to be occluded in the
second resistance change layer 4, the ions discharged from the
second resistance change layer 4 pass through the ion conductive
layer 3 to be occluded in the first resistance change layer 2.
[0042] By the situation in which the ions discharged from the first
resistance change layer 2 pass through the ion conductive layer 3
and are occluded in the second resistance change layer 4, the
resistance of the first resistance change layer 2 and the
resistance of the second resistance change layer 4 are both
decreased. By the situation in which the ions discharged from the
second resistance change layer 4 pass through the ion conductive
layer 3 and are occluded in the first resistance change layer 2,
the resistance of the first resistance change layer 2 and the
resistance of the second resistance change layer 4 are both
increased.
[0043] In the first resistance change layer 2 and second resistance
change layer 4, the resistance changes occur simultaneously at a
write time. In other words, the occlusion and the discharge of ions
in the two resistance change layers 2 and 4 occur simultaneously at
the write time when the resistance of each of the two resistance
change layers 2 and 4 is changed.
[0044] Note that the resistance change device 9 according to the
present embodiment is a resistance change device to which applied
is a configuration of a secondary battery to perform charge and
discharge by the movement of ions between a positive-electrode
active material layer and a negative-electrode active material
layer through an electrolytic layer. The secondary battery is also
referred to as a solid secondary battery or an ion battery.
[0045] That is, the positive-electrode active material layer and
the negative-electrode active material layer of the secondary
battery are used for the resistance change layers 2 and 4 which are
able to occlude and discharge ions of at least one type, and each
resistance of which changes in accordance with the amount of the
ions, and the electrolytic layer is used for the ion conductive
layer 3 configured to carry the ions.
[0046] In the present embodiment, the first resistance change layer
2 is a positive-electrode active material layer formed of a
positive-electrode active material used in the ion battery, the ion
conductive layer 3 is a solid electrolytic layer formed of a solid
electrolyte used in the ion battery, and the second resistance
change layer 4 is a negative-electrode active material layer formed
of a negative-electrode active material used in the ion
battery.
[0047] In other words, the resistance change device 9 of the
present embodiment is a resistance change device containing a solid
electrolytic material, and has a structure in which the solid
electrolytic layer (the ion conductive layer 3) is sandwiched
between the two resistance change layers (the first resistance
change layer 2 and second resistance change layer 4) as a
positive-electrode active material layer and a negative-electrode
active material layer.
[0048] Here, the first resistance change layer 2 is a
positive-electrode active material layer in which the resistance
decreases when the ions are discharged, and the resistance
increases when the ions are occluded.
[0049] The second resistance change layer 4 is a negative-electrode
active material layer in which the resistance increases when the
ions are discharged, and the resistance decreases when the ions are
occluded.
[0050] In this manner, in the case where the first resistance
change layer 2 is formed of a positive-electrode active material
whose resistance decreases when the ions are discharged the second
resistance change layer 4 is formed of a negative-electrode active
material whose resistance decreases when the ions are occluded.
[0051] In the case where the first resistance change layer 2 is
formed of a positive-electrode active material whose resistance
increases when the ions are occluded, the second resistance change
layer 4 is formed of a negative-electrode active material whose
resistance increases when the ions are discharged.
[0052] Not being limited to the above, the first resistance change
layer 2 may be a negative-electrode active material layer whose
resistance decreases when the ions are discharged and increases
when the ions are occluded, and the second resistance change layer
4 may be a positive-electrode active material layer whose
resistance increases when the ions are discharged and decreases
when the ions are occluded.
[0053] That is, in the case where the first, resistance change
layer 2 is formed of a negative-electrode active material whose
resistance decreases when the ions are discharged, the second
resistance change layer 4 may be formed of a positive-electrode
active material whose resistance decreases when the ions are
occluded.
[0054] In the case where the first resistance change layer 2 is
formed of a negative-electrode active material whose resistance
increases when the ions are occluded, the second resistance change
layer may be formed of a positive-electrode active material whose
resistance increases when the ions are discharged.
[0055] As described above, one of the first resistance change layer
2 and second resistance change layer 4 formed of the
positive-electrode active material or negative-electrode active
material discharges ions, and the other one of them occludes
ions.
[0056] For example, in a case of using Li ions, the
negative-electrode active, material forming the second resistance
change layer 4 may use Li.sub.4Ti.sub.5O.sub.12 or the like
configured to decrease the resistance when the Li ions are
occluded, the solid electrolyte forming the ion conductive layer 3
may use Li.sub.3PO.sub.4,
Li.sub.9Al.sub.3(P.sub.2O.sub.7).sub.3(PO.sub.4).sub.2,
Li.sub.2.9PO.sub.3.3N.sub.0.46, (La, Li)TiO.sub.3 or the like, and
the positive electrode active material forming the first resistance
change layer 2 may use LiCoO.sub.2, LiNiO.sub.2,
LiTi.sub.5O.sub.12, LiMnO.sub.2, LiFePO.sub.4 or the like
configured to decrease the resistance when the Li ions are
discharged.
[0057] Ions other than Li ions may be used.
[0058] In the present embodiment, the resistance change device 9
includes, as illustrated in FIG. 1, a first electrode 5 and a
second electrode 6 that are provided separate from each other to be
connected to the first resistance change layer 2, and a third
electrode 7 and a fourth electrode 8 that are provided separate
from each other to be connected to the second resistance change
layer 4.
[0059] Here, the first electrode 5 and second electrode 6 are
disposed under the first resistance change layer 2 as the
lower-side resistance change layer. The third electrode 7 and
fourth electrode 8 are disposed above the second resistance change
layer 4 as the upper-side resistance change layer.
[0060] When information (resistance value) is to be written, a
write voltage may be applied to the first resistance change layer 2
and second resistance change layer 4 via at least one of the first
electrode 5 and second electrode 6 and via at least one of the
third electrode 7 and fourth electrode 8, and the information may
be written by causing the resistance of the first resistance change
layer 2 and second resistance change layer 4 to change.
[0061] Here, by applying a positive voltage to at least one of the
first electrode 5 and second electrode 6 and by grounding at least
one of the third electrode 7 and fourth electrode 8, or by
grounding at least one of the first electrode 5 and second
electrode 6 and by applying a positive voltage to at least one of
the third electrode 7 and fourth electrode 8, the write voltage may
be applied to the first resistance change layer 2 and second
resistance change layer 4.
[0062] When information (resistance value) is to be read out, a
read voltage may be applied to the first resistance change layer 2
via the first electrode 5 and second electrode 6, and the read
voltage may also be applied to the second resistance change layer 4
via the third electrode 7 and fourth electrode 8; then the
information may be read out by detecting a current flowing through
the first resistance change layer 2 and second resistance change
layer 4.
[0063] Here, as illustrated in FIG. 2, the first resistance change
layer 2 and second resistance change layer 4 are connected in
parallel, and the read voltage is applied to the first resistance
change layer 2 and second resistance change layer 4 to detect a
current (readout current) flowing through the first resistance
change layer 2 and second resistance change layer 4, thereby
reading out the information (resistance value).
[0064] As described above, the first electrode 5 and second
electrode 6 used for reading out a resistance value of the first
resistance change layer 2 are disposed separate from each other,
and the third electrode 7 and fourth electrode 8 used for reading
out a resistance value of the second resistance change layer 4 are
disposed separate from each other.
[0065] This makes it possible to obtain a change in resistance
sufficient to function as the resistance change device 9, and
improve characteristics thereof.
[0066] In contrast, in a case where an electrode used for reading
out the resistance value of the resistance change layer is provided
over the entire surface of the resistance change layer, the
resistance change become small, which makes it difficult to obtain
a change in resistance sufficient to function as a resistance
change device.
[0067] That is, in a case where a positive-electrode active
material, which is a material having high resistivity, is used in a
secondary battery, an electrode layer is laminated on the
positive-electrode active material layer to be provided over the
entire surface of the positive-electrode active material layer.
Since the resistance value is lowered in this manner, no problem
occurs.
[0068] However, in a case where a positive-electrode active
material is used as a resistance change layer, when an electrode
layer is laminated on the resistance change layer to be provided
over the entire surface of the resistance change layer, the
resistance change is given by combined resistance of the resistance
change layer and the electrode layer having low resistivity. This
may cause the resistance change to be small.
[0069] Accordingly, it is difficult to obtain a change in
resistance sufficient to function as a resistance change
device.
[0070] Further, in the case where information (resistance value) is
read out in the manner discussed above, a combined resistance value
(combined resistance) of the resistance values of the first
resistance change layer 2 and second resistance change layer 4 is
read out as information (resistance value) stored in the resistance
change device 9.
[0071] In other words, when information is to be read out, the
reading of the information is performed by detecting a current
(readout current) flowing through the two resistance change layers
2 and 4, and determining a resistance value (combined resistance
value) based on the detected current. Accordingly, it is possible
to cause the current (readout current) flowing through the
resistance change device 9 to be large when the information is read
out.
[0072] This makes it possible to obtain a sufficient readout
current, and suppress malfunctioning such as making a wrong
determination of whether a resistance value stored as information
is "0" or "1", for example, thereby making it possible to improve
the characteristics.
[0073] Hereinafter, description will be given while citing specific
examples.
[0074] When information (resistance value) is to be written, that
is, when a resistance value of the resistance change device 9
(device resistance) is to be changed, a voltage for causing ions to
move (write voltage) may be applied between one or both of the
first and second electrodes 5, 6 and one or both of the third and
fourth electrodes 7, 8, and the information may be written by
causing the resistance (resistance value) of each of the first
resistance change layer 2 and second resistance change layer 4 to
change.
[0075] For example, in a case where LiCoO.sub.2 as a
positive-electrode active material is used for the first resistance
change layer 2 in the lower layer and Li.sub.4Ti.sub.5O.sub.12 as a
negative-electrode active material is used for the second
resistance change layer 4 in the upper layer, the write voltage may
be applied to the first resistance change layer 2 and second
resistance change layer 4 by applying a positive voltage to the
first electrode 5 and second electrode 6, and grounding the third
electrode 7 and fourth electrode 8.
[0076] With this, Li ions move from LiCoO.sub.2 forming the first
resistance change layer 2 toward Li.sub.4Ti.sub.5O.sub.12 forming
the second resistance change layer 4 so that the resistance
(resistance value) of each of the first resistance change layer 2
and second resistance change layer 4 is changed, whereby the
writing of the information is performed.
[0077] On the other hand, by applying a positive voltage to the
third electrode 7 and fourth electrode 8 and grounding the first
electrode 5 and second electrode 6, the write voltage may be
applied to the first resistance change layer 2 and second
resistance change layer 4.
[0078] With this, the Li ions move from Li.sub.4Ti.sub.5O.sub.12
forming the second resistance change layer 4 toward LiCoO.sub.2
forming the first resistance change layer 2 so that the resistance
(resistance value) of each of the first resistance change layer 2
and second resistance change layer 4 is changed, whereby the
writing of the information is performed.
[0079] When the writing of the information is performed as
discussed above, the amount of resistance change of the first
resistance change layer 2 and second resistance change layer 4
varies in accordance with the amount of movement of the Li ions. In
other words, the amount of a change in combined resistance of the
first resistance change layer 2 and second resistance change layer
4, that is, the amount of a change in resistance of the resistance
change device 9 varies in accordance with the amount of movement of
the Li ions.
[0080] It is possible to control the amount of movement of the Li
ions by a voltage applied between the first and second electrodes
5, 6 and the third and fourth electrodes 7, 8, the number of
pulses, a pulse time, and the like.
[0081] FIG. 3 is a graph depicting a resistance change of the
resistance change device according to the present embodiment.
[0082] In FIG. 3, a solid line A indicates a change in device
resistance of the resistance change device 9 of the present
embodiment (for example, see FIG. 1).
[0083] A solid line B in FIG. 3 indicates a change in device
resistance of a resistance change device of related art, that is, a
change in device resistance of a resistance change device 11 (for
example, see FIG. 4) that is provided with an Li layer (an Li
metal, which is an ion occlusion and discharge layer) 10 in place
of the second resistance change layer 4 in the upper layer of the
resistance change device of the present embodiment, and is provided
with only a resistance change layer 2 in the lower layer as a
resistance change layer.
[0084] Note that in the resistance change device 9 of the present
embodiment, a change in device resistance is a change in combined
resistance of the resistance change layer 4 in the upper layer and
the resistance change layer 2 in the lower layer; on the other
hand, in the resistance change device 11 of related art, a change
in device resistance is only a change in resistance of the
resistance change layer 2 in the lower layer.
[0085] In FIG. 3, "two-minute charge" refers to a case in which a
positive voltage is applied to the first electrode 5 and second
electrode 6, the third electrode 7 and fourth electrode 8 are
grounded, and a charging current of 2 .mu.A is flowed for two
minutes.
[0086] In this case, Li ions move from LiCoO.sub.2 forming the
first resistance change layer 2 in the lower layer toward
Li.sub.4Ti.sub.5O.sub.12 forming the second resistance change layer
4 in the upper layer so that the resistance (resistance value) of
each of the first resistance change layer 2 and second resistance
change layer 4, that is, the resistance value (device resistance)
of the resistance change device 9 is changed, whereby the writing
of the information is performed.
[0087] In FIG. 3, "one-minute discharge" refers to a case in which
the first electrode 5 and second electrode 6 are grounded, a
positive voltage is applied to the third electrode 7 and fourth
electrode 8, and a discharging current of 2 .mu.A is flowed for one
minute.
[0088] In this case, Li ions move from Li.sub.4Ti.sub.5O.sub.12
forming the second resistance change layer 4 in the upper layer
toward LiCoO.sub.2 forming the first resistance change layer 2 in
the lower layer so that the resistance (resistance value) of each
of the first resistance change layer 2 and second resistance change
layer 4, that is, the resistance value (device resistance) of the
resistance change device 9 is changed, whereby the writing of the
information is performed.
[0089] First, the resistance value of the resistance change device
9 of the present embodiment and the resistance value of the
resistance change device 11 of related art were measured. These
values were taken as initial values.
[0090] Next, charging was performed for two minutes, and the
resistance value of the resistance change device 9 of the present
embodiment and the resistance value of the resistance change device
11 of related art were measured.
[0091] Subsequently, charging was further performed for five
minutes, and the resistance value of the resistance change device 9
of the present embodiment and the resistance value of the
resistance change device 11 of related art were measured.
[0092] Next, discharging was performed for one minute, and the
resistance value of the resistance change device 9 of the present
embodiment and the resistance value of the resistance change device
11 of related art were measured.
[0093] Finally, discharging was performed for one minute, and the
resistance value of the resistance change device 9 of the present
embodiment and the resistance value of the resistance change device
11 of related art were measured.
[0094] The measurement results of the resistance values obtained in
the above manner are given in FIG. 3.
[0095] As depicted in FIG. 3, it was observed that, in, both the
resistance change device 11 of related art and the resistance
change device 9 of the present embodiment, the resistance value
decreased when charging was performed, and the resistance value
increased when discharging was performed.
[0096] The device resistance (resistance value) of the resistance
change device 11 of related art was on the order of 10.sup.5
.OMEGA. to 10.sup.7 .OMEGA., while the device resistance of the
resistance change device 9 of the present embodiment was on the
order of 10.sup.4 .OMEGA. to 10.sup.5 .OMEGA., and therefore it was
confirmed that an effect of a reduction in resistance value was
obtained by one to two orders.
[0097] The information (resistance value) may be written as
discussed above, and the information (resistance value) may be read
out in the following manner,
[0098] For example, as illustrated in FIG. 2, the first electrode 5
is connected to the third electrode 7 and the second electrode 6 is
connected to the fourth electrode 8 in such a manner that the first
resistance change layer 2 in the lower layer and the second
resistance change layer 4 in the upper layer are connected in
parallel.
[0099] Then, a read voltage (for example, about 0.1 V) is applied
between the first electrode 5 and second electrode 6 and between
the third electrode 7 and fourth electrode 8, that is, the read
voltage is applied to the first resistance change layer 2 and
second resistance change layer 4, and the information may be read
out by detecting a current (readout current) flowing through these
layers, that is, flowing through the first resistance change layer
2 and second resistance change layer 4.
[0100] When information is read out in the manner discussed above,
the combined resistance (combined resistance value) of the first
resistance change layer 2 and second resistance change layer 4,
that is, the resistance (resistance value) of the resistance change
device 9 is determined based on a combined current flowing through
the first resistance change layer 2 and second resistance change
layer 4, and the determined resistance read out a information
(resistance value) stored in the resistance change device 9.
[0101] Then, in the resistance change device 9 of the present
embodiment, when information is to be read out, by detecting a
current (readout current) flowing through the two resistance change
layers 2 and 4, and determining a resistance value (combined
resistance value) based on the detected current, the information is
read out Accordingly, the current (readout current) flowing through
the resistance change device may be made large when the information
is read out.
[0102] This makes it possible to obtain a sufficient readout
current, and suppress malfunctioning such as making a wrong
determination of whether a resistance value stored as information
is "0" or "1", for example, thereby making it possible to improve
the characteristics.
[0103] Note that in the resistance change, device 9 of the present
embodiment, it is possible to obtain the above-discussed effect of
the reduction in resistance value and also possible to obtain the
effect in which the readout current may be made large, the
occurrence of a malfunction may be suppressed, and the
characteristics thereof may be improved. In addition, the following
effects are also obtained.
[0104] In FIG. 5, charge and discharge characteristics of the
resistance change device 11 of related art (for example, see FIG.
4) are depicted. In FIG. 6, charge and discharge characteristics of
the resistance change device 9 of the present embodiment (for
example, see FIG. 1) are depicted.
[0105] Note that in the resistance change device 11 of related art
(for example, see FIG. 4), an operation to extract ions (elements)
from the resistance change layer 2 and decrease its resistance
value is referred to as "charge", and the charge characteristics
are indicated by a solid line A in FIG. 5.
[0106] Conversely, an operation to make ions (elements) enter the
resistance change layer 2 and increase its resistance value is
referred to as "discharge" and the discharge characteristics are
indicate by a solid line B in FIG. 5.
[0107] In the resistance change device 9 of the present embodiment
(for example, see FIG. 1), an operation to apply a positive voltage
to the side of the first resistance change layer 2 using a
positive-electrode active material among the two resistance change
layers 2 and 4, extract ions (elements) from the first resistance
change layer 2, make the ions (elements) enter the second
resistance change layer 4, and decrease the resistance value of the
first resistance change layer 2 and second resistance change layer
4 is referred to as "charge", and the charge characteristics are
indicated by a solid line A in FIG. 6.
[0108] Conversely, an operation to apply a positive voltage to the
side of the second resistance change layer 4 using a
negative-electrode active material among the two resistance change
layers 2 and 4, extract ions (elements) from the second resistance
change layer 4, make the ions (elements) enter the first resistance
change layer 2, and increase the resistance, value of the first
resistance change layer 2 and second resistance change layer 4 is
referred to as "discharge", and the discharge characteristics are
indicated by a solid line B in FIG. 6.
[0109] As depicted in FIG. 5, in the resistance change device 11 of
related art (for example, see FIG. 4), the charge and the discharge
are ended when a target voltage (3 V in FIG. 5) is generated
(portions indicated by arrows in FIG. 5), but the voltage does not
stay at the target voltage and a voltage return occurs.
[0110] This is called a relaxation phenomenon, and it occurs due to
a situation in which the ions having been taken in and out return
to the original positions after the charge and discharge having
been ended. Due to this phenomenon, the amount of ions (elements)
is deviated from the original target amount of ions in the
resistance change layer 2 so that the resistance value is
deviated.
[0111] In contrast, as depicted in FIG. 6, in the resistance change
device 9 of the present embodiment (for example, see FIG. 1), the
charge and the discharge are simultaneously performed in the two
resistance change layers 2 and 4, that is, the operation to extract
the ions and the operation to make the ions enter are carried out
simultaneously in the two resistance change layers 2 and 4. This
suppresses each relaxation phenomenon, and therefore an effect of
reducing the deviation relative to the target voltage (2 V in FIG.
6) caused by the above-mentioned-return is obtained
[0112] The voltage generated in the resistance change device 11 of
related art (for example, see FIG. 4) differs from the voltage
generated in the resistance change device 9 of the present
embodiment (for example, see FIG. 1) because their
negative-electrode active materials are different from each
other.
[0113] Next, a manufacturing method for the resistance change
device according to the present embodiment will be described.
[0114] The manufacturing method for the resistance change device
according to the present embodiment includes a process of forming
the first resistance change layer 2, a process of forming the ion
conductive layer 3, and a process of forming the second resistance
change layer 4 (for example, see FIG. 1).
[0115] In the process of forming the first resistance change layer
2, formed is the first resistance change layer 2 which is able to
occlude and discharge ions of at least one type, and the resistance
of which changes in accordance with the amount of the ions in such
a manner that the resistance decreases when the ions are discharged
and the resistance increases when the ions are occluded.
[0116] In the process of forming the ion conductive layer 3, the
ion conductive layer 3 configured to carry ions is formed on the
first resistance change layer 2.
[0117] In the process of forming the second resistance change layer
4, on the ion conductive layer 3, formed is the second resistance
change layer 4 which is able to occlude and discharge ions, and the
resistance of which changes in accordance with the amount of the
ions in such a manner that the resistance increases when the ions
are discharged and the resistance decreases when the ions are
occluded.
[0118] For example, in a case of using Li ions, it is possible to
manufacture the resistance change device 9 in the following manner:
a Pt/Ti layer (a Pt/Ti laminated film, which is a laminated film
where a Pt film is laminated on a Ti film in this case) as the
first electrode 5 and second electrode 6, an LiCoO.sub.2 layer as
the first resistance change layer 2, an Li.sub.3PO.sub.4 layer as
the ion conductive layer 3, an Li.sub.4Ti.sub.5O.sub.12 layer as
the second resistance change layer 4, and a TiN/Pt layer (a TiN/Pt
laminated film, which is a laminated film where a TiN film is
laminated on a Pt film in this case) as the third electrode 7 and
fourth electrode 8 are laminated on the substrate 1 by using masks
(for example, see FIG. 1).
[0119] Note that the third electrode 7 and fourth electrode 8 are
each formed of the TiN/Pt layer, where the TiN film is provided in
the upper-side layer. This is because the above constitution is
compatible with wiring provided on the electrodes 7 and 8. If the
above point is not taken into consideration for example, a Ti layer
or the like may be used instead.
[0120] The reason why the above-discussed configuration is employed
will be described below.
[0121] A technology called artificial intelligence (AI) has
attracted rising attention in recent years, and the development of
the technology has been accelerated vigorously. Among the
AI-related technologies, machine learning using basic learning data
is in the spotlight today.
[0122] In the machine learning, weighting is performed beforehand
in accordance with importance of each data element using basic
data. With the weighting, it becomes possible for the machine
itself to determine and predict results with respect to a large
amount of new data. Accordingly, the process of weighting is
considered as a significantly important process.
[0123] In order to perform weighting in a computer, there exists a
method in which the weights are stored in a memory.
[0124] However, there are problems that the processing speed is
lowered and that the power consumption is increased, because the
weights are read out every time.
[0125] As such, a method in which a resistance value change of a
resistance device is used for weights is under study. In other
words, it is a method that utilizes the following phenomenon for
weighting: a current flowing through the resistance device changes
in accordance with a resistance value change of the resistance
device.
[0126] This resistance device is required to be nonvolatile in
order to store the weights.
[0127] As nonvolatile resistance memories, there exist a
magnetoresistive random access memory (MRAM) making use of
magnetism, a phase change random access memory (PCRAM) making use
of a crystalline state, and a resistive random access memory
(ReRAM) making use of oxidation-reduction or the like.
[0128] It is preferable that the weighting be represented by
multiple values such as "0", "1", and "2" rather than two values
such as "0" and "1" from a viewpoint of making precise
predictions.
[0129] However, since the above-mentioned MRAM makes use of balance
and imbalance of magnetism, it takes only two values. Since the
above-mentioned ReRAM makes use of two states, that is, an oxide
state and a metal state, it is difficult to maintain an
intermediate state thereof. Likewise, since the above-mentioned
PCRAM makes use of a crystalline state and a non-crystalline state,
it is difficult to maintain an intermediate state thereof.
[0130] As such, it is considered to utilize the principle of a
secondary battery such as a lithium battery whose resistance value
continuously changes, that is, utilize the principle of a secondary
battery configured to charge and discharge by the movement of ions
between a positive-electrode active material layer and a
negative-electrode active material layer through an electrolytic
layer, and constitute a resistance change device by using the
configuration of the stated secondary battery.
[0131] For example, as illustrated in FIG. 4, it is considered to
constitute the resistance change device 11 by stacking, on a
substrate 1, two electrodes 5 and 6 (read electrodes), a
positive-electrode active material layer as the resistance change
layer 2, a solid electrolytic layer as an ion conductive layer 3,
and a negative-electrode active material layer as the ion occlusion
and discharge layer 10 (also serving as an electrode).
[0132] In this case, due to the movement of ions between the
positive-electrode active material layer 2 and the
negative-electrode active material layer 10 through the solid
electrolytic layer 3, the amount of ions in the positive-electrode
active material layer 2 varies and the resistance changes in
response to the variation in the amount of ions, which makes it
possible to cause the above configuration to function as the
resistance change device 11 by reading out the changed resistance
as a resistance value between the read electrodes 5 and 6.
[0133] For example, in a case where the configuration of a lithium
battery is used, an Li layer is used for the negative-electrode
active material layer 10, and an LiCoO.sub.2 layer is used for the
positive-electrode active material layer 2, when a positive voltage
is applied to two electrodes 5, 6 on the substrate 1 side and the
Li layer 10 as the negative-electrode active material layer, which
also serves as the electrode in the uppermost layer, is grounded,
Li is extracted from the LiCoO.sub.2 layer as the
positive-electrode active material layer 2 and is occluded
(absorbed) in the Li layer 10 through the solid electrolyte 3.
[0134] Conversely, when a positive voltage is applied to the Li
layer 10 as the negative-electrode active material layer, which
also serves as the electrode in the uppermost layer, and the two
electrodes 5, 6 on the substrate 1 side are grounded, Li is
desorbed from the Li layer 10 and is occluded (absorbed) in the
LiCoO.sub.2 layer as the positive-electrode active material layer 2
through the solid electrolyte 3.
[0135] In this case, a portion where the resistance is changed,
that is, a portion that functions as the resistance change, layer 2
is the LiCoO.sub.2 layer as the positive-electrode active material
layer, and its resistance value changes in accordance with the
amount of Li inside thereof.
[0136] This makes it possible to cause the above configuration to
function as the resistance change device 11 in the following
manner: Li in the LiCoO.sub.2 layer as the positive-electrode
active material layer 2 is taken in and out to vary the amount of
Li and change the resistance value in response to the variation in
the amount of Li, and then the resistance value of the LiCoO.sub.2
layer as the positive-electrode active material layer 2 is read out
as a resistance value between the read electrodes 5 and 6 disposed
on both sides thereof.
[0137] The solid electrolyte is an insulation material, and does
not carry electrons but allows Li ions to flow therein. An electric
current flows between the read electrodes 5 and 6, not through the
solid electrolytic layer 3 but through the positive-electrode
active material layer 2.
[0138] However, for the positive-electrode active material layer 2,
not a material having low resistivity (resistance value) such as a
metal, but a substance (material) having high resistivity
(resistance value) such as a transition-metal complex oxide is
used.
[0139] Due to this, in a case where the above substance is used as
the resistance change layer 2, the resistance becomes large and the
readout current becomes small so as to cause a malfunction.
Accordingly, it has been found that the configuration using such
substance is insufficient to function as the resistance change
device and that the desired characteristics may not be
obtained.
[0140] In order to increase the readout current, although it is
considered to raise a voltage to be applied, doing so is not
preferable because the power consumption is increased.
[0141] Further, it is also considered to increase the size of the
resistance change device 11 of related art discussed above (for
example, see FIG. 4), doing so is not preferable because the device
becomes large.
[0142] Although it is also considered to dispose the resistance
change devices 11 of related art (for example, see FIG. 4) being
aligned on a plane and connect these devices, doing so is not
preferable because the configuration thereof becomes large in
size.
[0143] Although it is also considered to pile up and stack the
resistance change devices 11 of related art (for example, see FIG.
4) and connect these devices, doing so is not preferable because
the configuration thereof becomes large in size and the process at
the time of manufacturing is difficult to carry out.
[0144] Furthermore, in the resistance change device 11 of related
art discussed above (for example, see FIG. 4), the
negative-electrode active material layer 10 is formed of an Li
layer; however, since Li is likely to react with moisture and
oxygen, it is difficult to handle in a semiconductor process of
manufacturing the resistance change device 11.
[0145] When moisture is present, Li easily reacts with nitrogen to
generate lithium nitride (Li.sub.3N). Further Li reacts with oxygen
to generate lithium oxide (Li.sub.2O).
[0146] In the above-described resistance change device 11 of
related art (for example, see FIG. 4), although the
negative-electrode active material layer 10 is formed of an Li
layer, a silicon (Si) layer, a graphite (C) layer or the like may
be used instead.
[0147] However, since the above-mentioned materials are also likely
to react with moisture and oxygen, it is difficult to handle in a
semiconductor process of manufacturing the resistance change
device.
[0148] Si is not affected by water, but is oxidized by oxygen to
form silicon oxide (SiO.sub.2), that is, an insulator. Graphite is
not affected by water, but is oxidized by oxygen to form a carbonic
acid gas (CO, CO.sub.2).
[0149] In order to solve the above problems, the above-described
configuration (for example, see FIG. 1) is employed.
[0150] With the employment of the above configuration, the
resistance change device 9 may be manufactured with ease, the
expansion in size is suppressed, the increase in power consumption
is suppressed, the overall resistance of the resistance change
device 9 may be lowered, the readout current may be made large when
the resistance value of the resistance change layers 2 and 4 is
read out, the occurrence of a malfunction is suppressed, and the
characteristics are improved, so that it is possible to cause the
above configuration to satisfactorily function as the resistance
change device 9.
[0151] Although not a complex compound but a simple elemental
substance such as lithium (Li), silicon (Si), or graphite (C) has
been used for a negative-electrode active material layer of a
resistance change device, it is difficult to use a
negative-electrode active material layer formed of these materials
as a resistance change layer.
[0152] For example, even if a negative-electrode active material
layer formed of Li occludes and discharges Li ions through a solid
electrolytic layer, a change in resistance does not occur since the
above Li ions are ions themselves. Accordingly, the
negative-electrode active material layer formed of Li may not be
used as a resistance change layer.
[0153] Further, a negative-electrode active material layer formed
of Si, for example, is not suited to be a resistance change layer
because an elemental substance of Si has significantly large
resistance (for example, resistivity of 10.sup.3 .OMEGA.cm) in a
semiconductor.
[0154] For example, a negative-electrode active material layer
formed of graphite is not suited to be a resistance change layer
because the resistance of graphite is too small (for example,
resistivity is 10.sup.-3 .OMEGA.cm) in contrast to Si.
[0155] In addition, since the materials such as lithium (Li),
silicon (Si), and graphite (C) are likely to react with moisture
and oxygen, it is difficult to handle in a semiconductor process of
manufacturing the resistance change device. Accordingly, it is
preferable to use an oxidized material (oxide compound) resistant
to moisture and oxygen for the negative-electrode active material
layer.
[0156] In the case where an oxidized material is used for the
negative-electrode active material layer, it is preferable that a
material whose resistance changes be used, the negative-electrode
active material layer also function as a resistance change layer,
and the resistance change device be such a resistance change device
that is provided with two resistance change layers.
[0157] This brings the following advantage in comparison with a
resistance change device provided with a single resistance change
layer.
[0158] That is, in the case of the resistance change device
provided with a single resistance change layer, if the resistance
of the resistance change layer does not change for some reason, the
resistance change device becomes a defective device instantly.
[0159] On the other hand, as in the embodiment discussed above (for
example, see FIG. 1), with the resistance change device 9 including
the two resistance change layers 2 and 4, even if one of the
resistance change layers does not change its resistance, it is
highly probable that the resistance change device changes the
resistance thereof as a whole as long as the other one of the
resistance change layers changes its resistance; because of this,
the resistance change device is still operable so that a situation
in which the resistance change device instantly becomes defective
may be suppressed.
[0160] Note that, in the case of a resistance change device
including two resistance change layers, if the same material is
used in the two resistance change layers and these two resistance
change layers are made to operate in the same manner, resistance
changes are canceled out in the two resistance change layers; as
such, the problem that the readout current becomes small may not be
solved.
[0161] For example, in a case where the same active material is
used for a positive-electrode active material layer and a
negative-electrode active material layer in order to make them
operate at a low voltage, and these materials are made to operate
in the same manner, resistance changes are canceled out in the
positive-electrode active material layer and the negative-electrode
active material layer; as such, the above-mentioned problem that
the readout current becomes small may not be solved.
[0162] Note that a storage apparatus may be configured to include
the resistance change device 9 constituted as described above.
[0163] In this case, for example, as illustrated in FIG. 7, a
memory device 22 may be configured in the following manner: the
resistance change devices 9 constituted as described above are
disposed to be aligned in array form, and pieces of wiring 16 to 21
are connected to the first electrode 5, second electrode 6, third
electrode 7, and fourth electrode 8 of each resistance change
device 9 via contact portions 12 to 15 respectively so that the
first resistance change layer 2 and second resistance change layer
4 are connected in parallel.
[0164] In FIG. 7, a current flow at a read time is indicated by an
arrow. Switches SW1 to SW13 illustrated in FIG. 8 are omitted in
FIG. 7. In FIG. 7, a reference sign 23 indicates an insulation
layer (interlayer film).
[0165] Further, the memory device 22 configured in this manner may
be provided with, as illustrated in FIG. 8, the switches SW1 to
SW13 constituted by transistors.
[0166] In FIG. 8, a black circle means a connection. Further, in
FIG. 8, reference signs L1 to L5 indicate wiring, and these pieces
of wiring L1 to L5 are constituted by the wiring 16 to 21 in FIG.
7.
[0167] For example, as illustrated in FIG. 9, a storage apparatus
24 may include, for example, the memory device 22 configured as
discussed above, a column selection unit 25, a line selection unit
26, a control unit 27, and a detection unit 28.
[0168] Then, any of the resistance-change devices 9 provided in the
memory device 22 is selected by the column selection unit 25 and
the line selection unit 26 based on a write command from the
control unit 27, and information (resistance value) may be written
into the selected resistance change device 9.
[0169] Here, the writing of information (resistance value) into the
selected resistance change device 9 is performed as follows.
[0170] First, a case in which ions (for example, Li ions) are moved
from the second resistance change layer 4 in the upper layer to the
first resistance change layer 3 in the lower layer so as to write
the information (resistance value) will be described.
[0171] In this case, as illustrated in FIG. 10, the switches SW2,
SW3, SW6, and SW8 constituted by the transistors are switched, so
that a positive voltage is applied to the third electrode 7 and
fourth electrode 8 connected to the second resistance change layer
4 in the upper layer, and the first electrode 5 and second
electrode 6 connected to the first resistance change layer 2 in the
lower layer are grounded.
[0172] That is, the switches SW2 and SW3 constituted by the
transistors are each set to an ON state to establish a conductive
path, and then the positive voltage as a write voltage is applied
to the wiring L1 and L2, thereby applying the positive voltage to
the third electrode 7 and fourth electrode 8.
[0173] Further, the switches SW6 and SW8 are each set to an ON
state to establish a conductive path, and then the wiring L3 and
wiring L4 are grounded to be at a zero potential, thereby the first
electrode 5 and second electrode 6 being grounded to be at a zero
potential.
[0174] With this, ions (for example, Li ions) are moved from the
second resistance change layer in the upper layer to the first
resistance change layer 2 in the lower layer, the amount of ions in
the first resistance change layer 2 and second resistance change
layer 4 are controlled, and then the resistance of each of the
first resistance change layer 2 and second resistance change layer
4 is changed, whereby the writing of information into the
resistance change device 9 is performed.
[0175] Next, a case in which ions (for example, Li ions) are moved
from the first resistance change layer 2 in the lower layer to the
second resistance change layer 4 in the upper layer so as to write
the information (resistance value) will be described.
[0176] In this case, as illustrated in FIG. 11, the switches SW4,
SW5, SW7, SW9, SW10, and SW12 constituted by the transistors are
switched, so that a positive voltage is applied to the first
electrode 5 and second electrode 6 connected to the first
resistance change layer 2 in the lower layer, and the third
electrode 7 and fourth electrode 8 connected to the second
resistance change layer 4 in the upper layer are grounded.
[0177] That is, the switches SW4, SW5, and SW7 constituted by the
transistors are each set to an ON state to establish a conductive
path, and then the positive voltage as a write voltage is applied
to the wiring L3 and L4, thereby applying the positive voltage to
the first electrode 5 and second electrode 6.
[0178] Further, the switches SW9, SW10, and SW12 are each set to an
ON state to establish a conductive path, and then the wiring L1 and
wiring L2 are grounded to be at a zero potential, thereby the third
electrode 7 and fourth electrode 8 being grounded to be at a zero
potential.
[0179] With this, ions (for example, Li ions) are moved from the
first resistance change layer 2 in the lower layer to the second
resistance change layer 4 in the upper layer, the amount of ions in
the first resistance change layer 2 and second resistance change
layer 4 are controlled, and then the resistance of each of the
first resistance change layer 2 and second resistance change layer
4 is changed, whereby the writing of information into the
resistance change device 9 is performed.
[0180] Since the information written into the resistance change
device 9 in the manner discussed above, a write circuit 29 is
configured to include the wiring 16 to 21, the wiring L1 to L5, the
switches SW1 to SW13, the column selection unit 25, the line
selection unit 26 and the control unit 27.
[0181] Further, any of the resistance change devices 9 provided in
the memory device 22 is selected by the column selection unit 25
and the line selection unit 26 based on a read command from the
control unit 27, and information (resistance value) may be read out
from the selected resistance change device 9 by the detection unit
28.
[0182] Here, the reading of the information (resistance value) from
the selected resistance change device 9 is performed by setting
each of the switches SW1, SW2, SW5, SW8, SW10, and SW13 constituted
by the transistors to an ON state, and then applying a read voltage
to the wiring L1, as illustrated in FIG. 12.
[0183] With this, as indicated by arrows in FIG. 12, a current
flows from the wiring LI, through the second resistance change
layer 4 in the upper layer, toward the wiring L2, wiring L5, and
wiring L4 in sequence.
[0184] Simultaneously with this, as indicated by arrows in FIG. 12,
a current flows from the wiring L1 toward the wiring L3, and then
flows toward the wiring L4 through the first resistance change
layer in the lower layer.
[0185] Then, the currents having flowed in the resistance change
layers 2 and 4 in the lower and upper layers join together in the
wiring L4.
[0186] The information (resistance value) is read out by detecting
the above joined current as a readout current by the detection unit
28 (for example, by the measurement with an ammeter).
[0187] Since the information is read out from the resistance change
device 9 in the manner discussed above, a read circuit 30 is
configured to include the wiring 16 to 21, the wiring L1 to L5, the
switches SW1 to SW13, the column selection unit 25, the line
selection unit 26, the control unit 27, and the detection unit
28.
[0188] In this case, the storage apparatus 24 is configured to
include the resistance change device 9 configured as described
above, the write circuit 29 connected to the resistance change
device 9 and configured to write information into the resistance
change device 9, and the read circuit 30 connected to the
resistance change device 9 and configured to read out information
from the resistance change device 9.
[0189] Then, the read circuit 30 configures the first resistance
change layer 2 and second resistance change layer 4 to be connected
in parallel, and applies a read voltage to the first resistance
change layer 2 and second resistance change layer 4 to detect a
current flowing through the first resistance change layer 2 and
second resistance change layer 4, thereby reading out the
information.
[0190] In the case where the resistance change device 9 includes
the first electrode 5 and second electrode 6 that are provided
separate from each other to be connected to the first resistance
change layer 2, and the third electrode 7 and fourth electrode 8
that are provided separate from each other to be connected to the
second resistance change layer 4, the write circuit 29 and the read
circuit 30 perform writing and reading in the following manner.
[0191] That is, the write circuit 29 applies a write voltage to the
first resistance change layer 2 and second resistance change layer
4 via at least one of the first electrode 5 and second electrode 6
and via at least one of the third electrode 7 and fourth electrode
8, and writes the information by changing the resistance of the
first resistance change layer 2 and second resistance change layer
4.
[0192] The read circuit 30 applies a read voltage to the first
resistance change layer 2 via the first electrode 5 and second
electrode 6, and also applies the read voltage to the second
resistance change layer 4 via the third electrode 7 and fourth
electrode 8, and reads out the information by detecting a current
flowing through the first resistance change layer 2 and second
resistance change layer 4.
[0193] Further, the write circuit 29 applies a positive voltage to
at least one of the first electrode 5 and second electrode 6 and
grounds at least one of the third electrode 7 and fourth electrode
8, or grounds at least one of the first electrode 5 and second
electrode 6 and applies a positive voltage to at, least one of the
third electrode 7 and fourth electrode 8, whereby the write circuit
29 applies a write voltage to the first resistance change layer 2
and second resistance change layer 4.
[0194] Therefore, the resistance change device, the manufacturing
method for the stated resistance change device, and the storage
apparatus according to the present embodiment are able to obtain a
sufficient readout current, and have an advantage of suppressing
the occurrence of a malfunction.
[0195] Although, in the above-described embodiment, the information
is read out by configuring the first resistance change layer 2 and
second resistance change layer 4 to be connected in parallel, the
configuration is not limited thereto.
[0196] For example, as illustrated in FIG. 13, the first resistance
change layer 2 and second resistance change layer 4 may be
configured to be connected in series, and a read voltage may be
applied to the first resistance change layer 2 and second
resistance change layer 4 to detect a current flowing through the
first resistance change layer 2 and second resistance change layer
4, whereby the information may be read out.
[0197] In this case, even if one of the two resistance change
layers 2 and 4 is short-circuited or is in a significantly low
resistance state for some reason, the resistance change device 9
functions normally as a whole when the other one of them has no
problem, thereby making it possible to suppress a situation in
which the resistance change device 9 instantly becomes a defective
device. The resistance change layer being short-circuited or being
in a significantly low resistance state is in the same state as
being merely wiring.
[0198] As discussed above, in order to suppress the situation where
the resistance change device 9 instantly becomes a defective
device, the first resistance change layer 2 and second resistance
change layer 4 may also be used in such a manner as to be connected
in series.
[0199] In the case where, as described above, the first resistance
change layer 2 and second resistance change layer 4 are connected
in series, the memory device 22 may be configured by connecting the
wiring 16 to 20 to the first electrode 5, second electrode 6, third
electrode 7, and fourth electrode 8 of the resistance change device
9 via the contact portions 12 to 15 respectively, as illustrated in
FIG. 14, for example.
[0200] In FIG. 14, a current flow at a read time is indicated by an
arrow. Switches SW14 to SW22 illustrated in FIGS. 15 to 17 are
omitted in FIG. 14. In FIG. 14, the reference sign 23 indicates an
insulation layer (interlayer film).
[0201] The memory device 22 configured in this manner may be
provided with, as illustrated'in FIGS. 15 to 17, the switches SW14
to SW22 constituted by transistors.
[0202] In FIGS. 15 to 17, a black circle means a connection.
Further, in FIGS. 15 to 17, the reference signs L1 to L4 indicate
wiring, and these pieces of ring L1 to L4 are constituted by the
wiring 16 to 20 in FIG. 14.
[0203] The storage apparatus 24 may include the memory device 22
configured as discussed above, the column selection unit 25, the
line selection unit 26, the control unit 27, and the detection unit
28 (for example, see FIG. 9).
[0204] Then, any of the resistance change devices 9 provided in the
memory device 22 is selected by the column selection unit 25 and
the line selection unit 26 based on a write command from the
control unit 27, and information (resistance value) may be written
into the selected resistance change device 9.
[0205] Here, the writing of information (resistance value) into the
selected resistance change device 9 is performed as follows.
[0206] First, a case in which ions (for example, Li ions) are moved
from the second resistance change layer 4 in the upper layer to the
first resistance change layer 2 in the lower layer so as to write
the information (resistance value) will be described.
[0207] In this case, as illustrated in FIG. 15, the switches SW14,
SW15, SW17, and SW20 constituted by the transistors are switched,
so that a positive voltage is applied to the third electrode 7 and
fourth electrode 8 connected to the second resistance change layer
4 in the upper layer, and the first electrode 5 and second
electrode 6 connected to the first resistance change layer 2 in the
lower layer are grounded.
[0208] That is, the switches SW14 and SW15 constituted by the
transistors are each set to an ON state to establish a conductive
path, and then the positive voltage as a write voltage is applied
to the wiring L1 and L2 thereby applying the positive voltage to
the third electrode 7 and fourth electrode 8.
[0209] Further, the switches SW17 and SW20 are each set to an ON
state to establish a conductive path, and then the wiring L3 and
wiring L4 are grounded to be at a zero potential, thereby the first
electrode 5 and second electrode 6 being grounded to be at a zero
potential.
[0210] With this, ions (for example, Li ions) are moved from the
second resistance change layer 4 in the upper layer to the first
resistance change layer 2 in the lower layer, the amount of ions in
the first resistance change layer 2 and second resistance change
layer 4 are controlled, and then the resistance of each of the
first resistance change layer 2 and second resistance change layer
4 is changed, whereby the writing of information into the
resistance change device 9 is performed.
[0211] Next, a case in which ions (for example, Li ions) are moved
from the first resistance change layer 2 in the lower layer to the
second resistance change layer 4 in the upper layer so as to write
the information (resistance value) will be described.
[0212] In this case, as illustrated in FIG. 16, the switches SW16,
SW18, SW19, SW21, and SW22 constituted by the transistors are
switched, so that a positive voltage is applied to the first
electrode 5 and second electrode 6 connected to the first
resistance change layer 2 in the lower layer, and the third
electrode 7 and fourth electrode 8 connected to the second
resistance change layer 4 in the upper layer are grounded.
[0213] That is, the switches SW16 and SW19 constituted by the
transistors are each set to an ON state to establish a conductive
path, and then the positive voltage as a write voltage is applied
to the wiring L3 and L4, thereby applying the positive voltage to
the first electrode 5 and second electrode 6.
[0214] Further, the switches SW18, SW21, and SW22 are each set to
an ON state to establish a conductive path, and then the wiring LI
and wiring L2 are grounded to be at a zero potential, thereby the
third electrode 7 and fourth electrode 8 being grounded to be at a
zero potential.
[0215] With this, ions (for example, Li ions) are moved from the
first resistance change layer 2 in the lower layer to the second
resistance change layer 4 in the upper layer, the amount of ions in
the first resistance change layer 2 and second resistance change
layer 4 are controlled, and then the resistance of each of the
first resistance change layer 2 and second resistance change layer
4 is changed, whereby the writing of information into the
resistance change device 9 is performed.
[0216] Since the information is written into the resistance change
device 9 in the manner discussed above, the write circuit 29 is
configured to include the wiring 16 to 20, the wiring L1 to L4, the
column selection unit 25, the line selection unit 26, and the
control unit 27.
[0217] Further, any of the resistance change devices 9 provided in
the memory device 22 is selected by the column selection, unit 25
and the line selection unit 26 based on a read command from the
control unit 27, and information (resistance value) may be read out
from the selected resistance change device 9 by the detection unit
28.
[0218] Here, the reading of the information (resistance value) from
the selected resistance change device 9 is performed by setting
each of the switches SW14, SW16, SW17, and SW18 constituted by the
transistors to an ON state, and then applying a read voltage to the
wiring L1, as illustrated in FIG. 17.
[0219] With this, as indicated by arrows in FIG. 17, a current
flows from the wiring L1, through the second resistance change
layer 4 in the upper layer, toward the wiring L2 and wiring L4 in
sequence, and further flows toward the wiring L3 through the first
resistance change layer 2 in the lower layer.
[0220] The current having flowed through the resistance change
layers 2 and 4 in the lower and upper layers flows in the wiring
L3.
[0221] The information (resistance value) is read out by detecting
this current as a readout current by the detection unit 28 (for
example, by the measurement with an ammeter).
[0222] Since the information is read out from the resistance change
device 9 in the manner discussed above, the read circuit 30 is
configured to include the wiring 16 to 20, the wiring L1 to L4, the
column, selection unit 25, the line selection unit 26, the control
unit 27, and the detection unit 28.
[0223] In this case, the storage apparatus 24 is configured to
include the resistance change device 9 configured as described
above, the write circuit 29 connected to the resistance change
device 9 and configured to write information into the resistance
change device 9, and the read circuit 30 connected to the
resistance change device 9 and configured to read out information
from the resistance change device 9.
[0224] Then, the read circuit 30 configures the first resistance
change layer 2 and second resistance change layer 4 to be connected
in series, and applies a read voltage to the first resistance
change layer 2 and second resistance change layer 4 to detect a
current flowing through the first resistance change layer 2 and
second resistance change layer 4, thereby reading out the
information.
[0225] In the case where the resistance change device 9 includes
the first electrode 5 and second electrode 6 that are provided
separate from each other to be connected to the first resistance
change layer 2, and the third electrode 7 and fourth electrode 8
that are provided separate from each other to be connected to the
second resistance change layer 4, the write circuit 29 and the read
circuit 30 perform writing and reading in the following manner.
[0226] That is, the write circuit 29 applies a write voltage to the
first resistance change layer 2 and second resistance change layer
4 via at least one of the first electrode 5 and second electrode 6
and via at least one of the third electrode 7 and fourth electrode
8, and writes the information by changing the resistance of the
first resistance change layer 2 and second resistance change layer
4.
[0227] The read circuit 30 applies a read voltage to the first
resistance change layer 2 via the first electrode 5 and second
electrode 6, and also applies the read voltage to the second
resistance change layer 4 via the third electrode 7 and fourth
electrode 8, and reads out the information by detecting a current
flowing through the first resistance change layer 2 and second
resistance change layer 4.
[0228] Further, the write circuit 29 applies a positive voltage to
at least one of the first electrode 5 and second electrode 6 and
grounds at least one of the third electrode 7 and fourth electrode
8, or grounds at least one of the first electrode 5 and second
electrode 6 and applies a positive voltage to at least one of the
third electrode 7 and fourth electrode 8, whereby the write circuit
29 applies a write voltage to the first resistance change layer 2
and second resistance change layer 4.
[0229] Note that the present disclosure is not limited to the
configurations described in the above embodiments, and may be
variously modified without departing from the spirit and scope of
the present disclosure.
[0230] All examples and conditional language provided herein are
intended for the pedagogical purposes of aiding the reader in
understanding the invention and the concepts contributed by the
inventor to further the art, and are not to be construed as
limitations to such specifically recited examples and conditions,
nor does the organization of such examples in the specification
relate to a showing of the superiority and inferiority of the
invention. Although one or more embodiments of the present
invention have been described in detail, it should be understood
that the various changes, substitutions, and alterations could be
made hereto without departing from the spirit and scope of the
invention.
* * * * *